甜玉米穗冰水預冷之熱傳模式

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作者: 李允中;李祉修
刊名: 農業機械學刊
期刊所屬國別:
出版年: 1994
關鍵字: 甜玉米;水冷;數學模式;Sweet corn;Hydrocooling;Mathematical model
摘要: 甜玉米非常容易因呼吸作用使品質變劣,一般常用水冷法來去除甜玉米的田間餘熱以降低呼吸率、減少呼吸熱。甜玉米的水冷法雖然常見,但水冷時的熱傳分析研究仍不多。本研究依照甜玉米苞葉、玉米粒與玉米穗軸物性的不同,將甜玉米模擬成三層同軸無限圓柱。以三組邊界條件耦合的擴散方程式組來描述各層的熱傳遞,模式的熱擴散方程式組以正交展開通式法求得其解析解;模式中各層的熱傳導係數以高速水流冷卻的玉米穗之實驗數據推估,因此時表面熱傳遞係數的影響可以忽略。利用實驗室小規模的淋水式水冷機進行甜玉米穗的水冷實驗時,並建立一個二維的數學模式,實驗所得的數據與數值模擬的結果相當符合。Sweet corn deteriorates very easily due to its high respiration rate. Hydrocooling is often used to remove field heat thus to decrease respiration rate and heat. Although it is a common practice, heat transfer during hydrocooling is not fully exposed. In the study, sweet corn ear was modeled by a three-layer coaxial infinite cylinderical shell based on different physical properties of husk, kernels and cob. Heat transfer process in the corn ear was described by three diffusion equations with coupled boundary conditions. Heat diffusion equations of the model was analytically solved by the generalized orthogonal expansion technique. Thermal conductivities of each layer were estimated from the cooling experiments conducted at very high flow rate of cooling water to eliminate effects of the surface heat transfer coefficient. The cooling rates of sweet corn ears in a laboratory scale flooding type hydrocooler at different water flow rates were studied, and a two-dimensional model was developed. Data from the experiments and numerical simulations by the model were compared, fairly close results were obtained.
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